The actor Leonardo DiCaprio spoke during a meeting on Friday at the Paris climate talks.Credit
Thierry Chesnot/Getty Images

PARIS — Mayors from Los Angeles, Berlin, Madrid, Johannesburg and other major cities around the world gathered on Friday at City Hall in Paris to discuss their role in averting a climate catastrophe, but the star attraction was the actor Leonardo DiCaprio.

“Our world leaders are here in Paris in an effort to finalize a global agreement 20 years in the making, to finally address the very real threat that climate change poses to our planet,” Mr. DiCaprio told the mayors. “These leaders have met before. They met in Kyoto, they met in Copenhagen, and in cities on every continent, but each and every time, they have come up short. This time must be different, because we are fundamentally running out of time.”

He added: “Climate change is the most fundamental and existential threat to our species. The consequences are unthinkable and worse, it has the potential to make our planet unlivable.”

Mr. DiCaprio has been a spokesman for the movement to urge pension funds and other asset managers to divest from the coal, oil and gas industries. “Our future will hold greater prosperity and justice when we are free from the grip of fossil fuels,” he told the mayors. “Now to get there, we must act. We must finally leave behind the inefficient technologies of another century and the business models that they have created.”

The mayors had gathered here for the Climate Summit for Local Leaders, an event hosted by Mayor Anne Hidalgo of Paris and Michael R. Bloomberg, the former mayor of New York City and the United Nations secretary general’s special envoy for cities and climate change.

“You were not elected to ask the public where they want to go,” Mr. Bloomberg said to the mayors. “You were elected to have a vision about what is right for the people you serve, and then to convince them to follow you to a better life.”

St.-Denis is the northern suburb where one of the planners of the Paris terrorist attacks died in a police raid. Another attacker lived nearby, in Drancy; yet another rented a flat in neighboring Bobigny. A little further to the east is Clichy-sous-Bois, where riots started in 2005.

These suburbs are all part of Seine-St.-Denis, a tiny, densely populated administrative area northeast of Paris that is known for its leftist politics, its large immigrant population and, now, its links to extremist violence. (It is often referred to as the 93, after the first two digits of its postal codes.) The local annual income here is 16,000 euros, about $17,500, compared with the national average of 22,000 euros, or about $24,100. The unemployment rate is 13 percent, compared to the national average of around 10 percent.

Seine-St.-Denis is also home to Le Bourget, the suburb where the United Nations climate conference is being held. Local officials had hoped that the climate conference, also known as COP 21, would give its 40,000 visitors a more balanced sense of the area, and help it shed its rough image.

But with a national state of emergency still in effect, the Parc des Expositions, the convention center where the talks are being held, has become a tightly guarded fortress.

Shuttle buses take the throngs of negotiators, activists, scientists and journalists here directly to and from the nearby Métro and suburban train stations. Another set of shuttle buses travel to and from the hotels around Charles de Gaulle Airport, which is also in Seine-St.-Denis. And the talks themselves are closed to the public.

But there are a few spaces that welcome the ordinary visitor — and that give a chance for Seine-St.-Denis to present its story.

“It was really important for us to show that the town of Seine-St.-Denis continues living and that good things also happen in the suburbs,” said Jean-Luc Parisot, deputy director for economic development and employment in Seine-St.-Denis. “We are fed up with being stigmatized as only zones of trouble and poverty.”

In 2010, Seine-St.-Denis adopted a climate and energy plan, vowing to reduce emissions and to be less wasteful, particularly in the area of construction. (It is one of the only urban sites in Natura 2000, a European network of nature protection areas.)

Nearby, Guy Zard, who works in sales of green technology, showed off a new contraption: a so-called eco-cleaner that composts both vegetable and animal waste. The machine accelerates the composting process, which ordinarily takes months, through a combination of heat and microorganisms.

“These are the leftovers from your last burgers and French fries,” Mr. Zard said, while crumbling in his hands a brown powder that smelled like brown sugar. The powder, the end product of the machine, is used to enrich soil, like any other compost.

Touring the Gallery of Solutions on Wednesday, Ms. Royal, the French ecology minister, expressed interest in getting one of the machines for the building that houses her ministry.

Near them, a man wearing a safety helmet, Thierry Hatat, pressed the pedal of a machine with a small solar panel on top. The machine cleans paint from brushes on construction sites with far less water than is typically used. Instead of an oil-based solvent, it uses an organic solvent made from corn.

“The goal was zero carbon, zero waste, and we almost did it,” said Mr. Hatat, who invented the machine.

A local businessman, Youness Bourimech, was at the Gallery of Solutions. Born and raised in Bondy, in the center of Seine-St.-Denis, Mr. Bourimech began as an employee in a cleaning company and he now manages 15 employees at six companies, three of which focus on green construction methods.

“It is not easy with everything that has happened these last weeks, the police searches, the raids, the investigations, but we can’t get discouraged,” Mr. Bourimech said. “I am a guy from ‘les quartiers,’ as we say here, and I succeeded. Every teenager in Seine-St.-Denis deserves the same.” “Les quartiers” roughly translates as “the streets.”

Mr. Parisot, the local official, said that 29 percent of young people in Seine-St.-Denis were under the age of 20. Green jobs, he said, do not only involve manual labor like trash recycling or construction tasks.

“This new eco-friendly washing machine for paint brushes, for instance, it needs young people to work with it, and to invent more like it,” Mr. Parisot said. “We have jobs, but we don’t have the workers to fill them.”

A hacked Volkswagen ad at a Paris bus stop created by the eco-activists at Brandalism.Credit
Brandalism

The sleek Volkswagen Passat featured on the bus stop billboard of a Paris street corner sports a turbocharged engine, collision warning and touch-screen dashboard controls. But the ad is fake, and it isn’t designed to seduce aspiring drivers. It’s meant to shame.

It’s a pointed dig at the carmaker’s efforts to foil emissions tests by using illegal software, leading to recalls of millions of cars around the world. The message was crafted by the eco-activists at Brandalism, who said they had “reclaimed” more than 600 outdoor advertising spaces during the Paris climate change conference.

Last Friday, activists armed with four-way utility keys and instructions from the group’s website opened bus stands owned by JCDecaux, an outdoor advertising group, and replaced its ads with posters criticizing corporations and world leaders.

Volkswagen was targeted, activists said, because it is guilty of corporate greenwashing, a term used to describe companies that portray themselves as more eco-minded than their practices might otherwise suggest.

“Corporations are lining up with politicians to tell us they are part of the solution to the climate crisis and that we should trust them with their new technology, that they will save the day,” said Luke Tennison, a member of Brandalism, which describes itself as a guerrilla art movement fighting “against corporate control of the visual realm.” (Its name is a combination of the words “branding” and “vandalism.”)

“For us it shows that these companies cannot be trusted,” Mr. Tennison said.

The 150 alternative ads that the Brandalism artists created are a more subtle form of protest than marches, which were barred when France declared a state of emergency after the Paris attacks.

“Following the tragic events on 13th November in Paris, the government has chosen to ban the big civil society mobilizations — but big business events can continue,” Bill Posters, another member of the group, said in a statement. “Communities directly impacted” by the actions of corporations could not be heard, he said.

The Volkswagen posters were produced by the studio of Jonathan Barnbrook, a designer famous mostly for his commercial work (he recently created the cover art for David Bowie’s new album).

“We do those posters not as a design company but as citizens hoping for a better world and hoping for politicians to act,” Mr. Barnbrook said.

Volkswagen, which declined to comment on the fake ads, is not the only corporation targeted by Brandalism. A fake ad criticizing Mobil reads: “We knew about the impact of fossil fuel but publicly denied it.”

Air France, one of the main sponsors of the climate talks, received a particular damning tagline: “Tackling climate change? Of course not. We’re an airline.” The poster is illustrated with a picture of a flight attendant putting a finger to her lips, smiling secretively.

Some of the world leaders arriving in Paris over the weekend might have spotted their own faces on billboards. Prime Minister Shinzo Abe of Japan had cooling towers growing out of his head on one poster. And Prime Minister David Cameron of Britain was depicted wearing a Formula One driver’s suit featuring corporate sponsorship tags by Shell, British Gas and The Sun, the popular British tabloid.

Most of the posters were taken down over the weekend, before the conference officially started, but some made it until this week.

James E. Hansen at his farm in Pennsylvania, in 2013.Credit
Michael Nagle for The New York Times

LE BOURGET, France — James E. Hansen, the retired NASA climate scientist, issued a stark warning Wednesday that the deal being negotiated here was nowhere close to what was needed to avert dangerous levels of global warming.

“This is half-assed and it’s half-baked,” Dr. Hansen said in a public forum on the sidelines of the conference. He said that the deal, praised by world leaders including President Obama, would allow emissions to continue to increase — until 2030, in the case of China — when what was needed is an immediate and rapid reduction.

The remarks were less notable for what Dr. Hansen said – he has long held a dim view of United Nations climate talks – than for where and when he said them.

Dr. Hansen, who retired in 2013 after decades in charge of the NASA Goddard Institute for Space Studies in New York, was making his first appearance at one of the annual U.N. climate conferences. He was introduced as “the Paul Revere of the climate-change movement” before a public interview for a video program.

Dr. Hansen, 74, gained fame in 1988 for warning the United States Congress that global warming had already begun and was a grave threat to future generations. He has been a voice in the wilderness ever since, and the failure of politicians to take the issue seriously has radicalized him. He regularly turns up at climate demonstrations, and has made a point of getting arrested several times.

In his appearance Wednesday, Dr. Hansen dismissed the emerging deal and said the willingness of most countries to offer some kind of emissions reductions was insufficient. Only a handful of countries are responsible for the bulk of emissions, and Dr. Hansen instead called for an agreement among those countries to begin an urgent assault on the problem.

“I’ve met with captains of industry,” Dr. Hansen said. “These people have children and grandchildren. They would like to be part of the solution, if the government would give them the right incentives.”

He repeated his longstanding position that the place to start would be a tax on carbon emissions that would raise the price of high-carbon fuels enough to encourage conservation and a switch to alternative energy sources. The money raised by such a tax should be given back to the public, he said.

Dr. Hansen also supports expansion of nuclear power as a partial solution to the climate crisis, and is expected to join other pro-nuclear scientists in an appearance later in the week. His nuclear stance has put him at odds with some environmental groups, though most of them still regard him as a hero for his warnings about the potential consequences of unchecked warming.

Dr. Hansen sketched out a future of profound climate threats that he said was on the verge of becoming unstoppable, including a potential collapse of the West Antarctic ice sheet, which could cause a rise in the sea levels sufficient to drown many coastal regions.

“Our parents did not know that they were causing a problem for future generations by burning fossil fuels,” Dr. Hansen said. “But we can only pretend we do not know.”

Reporting at climate negotiations often requires athletic prowess. Tracking important figures as they are coming and going from meetings — inevitably at opposite ends of a vast convention center — means regular sprints from one end corner to the other of a stadium-size venue to catch your subjects for fresh quotes and updates.

Inevitably, the talks go into overtime. Much like college students and Congress, United Nations negotiators are notorious for leaving everything to the last minute.

Read more about Coral Davenport’s experiences covering United Nations climate change negotiations — when diplomats negotiate through the night, and the reporters stay, too.

President Dilma Rousseff of Brazil arrived for the opening of the climate conference on Monday in Le Bourget, outside Paris.Credit
Loic Venance/Agence France-Presse — Getty Images

LE BOURGET, France — The American writer and activist Rebecca Solnit popularized the term “mansplaining” — to explain (something) to someone, often a woman, in a condescending or patronizing manner.

That was not exactly what was happening on Monday, as 150 world leaders addressed the Paris climate talks. But there were certainly a lot of men. And there was a lot of explaining going on.

The few female speakers included Presidents Dilma Rousseff of Brazil and Park Geun-hye of South Korea; Chancellor Angela Merkel of Germany; and Christiana Figueres, executive secretary of the United Nations Framework Convention on Climate Change.

The speeches were plentiful, coming one after the other, and became increasingly predictable, even formulaic, as the day wore on:

Thank the French hosts for going through with the meeting, just two weeks after the Paris terrorist attacks.

Note the urgency of collective action on perhaps the greatest problem that faces all of humanity.

Reiterate the need for a comprehensive, binding, fair and balanced agreement.

Point to what his or her own country is doing — the so-called Intended Nationally Determined Contributions — to help out.

Ms. Solnit, who has been reporting on climate change for Harper’s, said she did not feel the session was particularly egregious in terms of gender. The greater crime, she said, was its banality.

“It’s a parade of clichés,” she said.

President Janos Ader of Hungary stood out, she said, for at least attempting to speak from the heart and deliver a jargon-free address. Mr. Ader said he was haunted by the thought that his grandchild would some day ask him: “Grandpa, why did you let this happen? Why didn’t you act in time?”

“It was really basic,” Ms. Solnit said of his speech, “except that, compared to everybody else’s, it at least had some literary dimension.”

She added: “They’re all saying the right thing.” But when it came to the substance of the event — the need to reel in carbon emissions — there were disparities in the baseline levels they cited in making their promises to curb greenhouse gas emissions by 2030, she said.

“What makes me crazy is that Obama and Putin are talking about 2005 levels, and the European Union is talking about 1990 levels,” she said. “It’s like gaining 100
pounds and then boasting that you’re losing 50.”

Several recent studies that looked at the individual national plans found that they would cumulatively lead to a temperature increase of 5 to 6 degrees Celsius — well over the maximum of 2 degrees Celsius (3.6 degrees Fahrenheit) that is the goal of the meeting.

Ms. Solnit found the speeches “sort of homogeneous.”

“They are all saying these blandly positive things about commitment, verification, and science,” she said. “It doesn’t really add up to anything interesting.”